It is common practice to install a lock on a door in order to prevent strangers from intruding into a private space, an office, etc. However, conventional locks, for example, a mechanical lock with a physical key and an electronic lock with an electronic key (e.g., a password, a keycard, etc.), have some disadvantages. For example, the conventional mechanical lock cannot be released if the unique physical key is lost, and the conventional electronic lock cannot be released if the unique keycard is lost or the password has been forgotten. There is another conventional electronic lock that can be released by biometric verification.